In a magnetic data storage and retrieval system, a magnetic read/write head typically includes a writer portion having a magnetoresistive (MR) sensor for retrieving magnetically encoded information stored on a magnetic disc. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. The change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover the information encoded on the disc
Unfortunately, these data storage devices often experience specific errors and failure modes due to an undesired magnetic flux originating from a location of the read/write head. It is not uncommon for a magnetic domain, or domain wall (DW), to form in shield(s) of the read/write head. This phenomenon can dynamically vary during various operations conducted by the read/write head and result in sporadic and inconsistent reading and/or writing failures. For example, a DW can cause magnetic flux writing and/or erasing of information contained on media in an undesirable and often uncontrollable manner. Additionally and alternately, if a DW is close to the read head itself, the magnetic field caused by the DW itself can directly affect the accuracy of the readout.
Prior to being assembled into the data storage device, domain walls are removed from the read/write head. However, during use of the data storage device, it is not uncommon for domain walls to reform and reappear.